There has been a constant endeavor to increase the time between overhaul of jet engines that power aircraft and to reduce smoke and pollutants emitted into the atmosphere. This invention addresses itself to both of these problems.
As is well known, thrust of the engine can be increased by adding water to the burner section. In fuel nozzles for certain engines both the primary and secondary fuels are injected into the burner in conically radiating spray patterns that are in coaxial relationship. Such nozzles are, for example, utilized on the JT-9D engine manufactured by Pratt & Whitney Aircraft Group of United Technologies Corporation, the assignee of this patent application and the details of which are incorporated herein by reference. In this configuration, water is admitted upstream of the fuel spray and passes through the fuel support heat shields prior to being injected into the burner section via the burner swirlers. The problem with this configuration is that a significant deterioration in burner performance was evidenced. Also, this type of water injection system manifested a high smoke density, produced excessive hot spots at the turbine inlet as well as excessive distortions of the turbine inlet temperature radial profile.
It is also well known that fuel and air are injected into a burner with a tangential component so as to achieve a fast and complete mixing. Since water is admitted upstream of the juncture where it mixes with the fuel, it is carried in the airstream and assumes the same rotational direction. Hence, the fuel nozzle contains spin slots and vanes that are designed to impart a swirl to both the fuel and air. Further, the fuel nozzle is designed so that the fuel and air pattern in the burner combustion zone take the form of cones radiating from the apex as it leaves the fuel nozzle and flares into a cone as it propagates downstream in the burner.
In heretofore nozzle configurations it has been conventional to impart the swirl of the fuel in a direction that is counter to the direction of the swirl of the air.
We have found that we can obviate the problems noted above in the water injection mode by changing the relationship of the direction of the swirl so that the fuel and air/water mixture both swirl in the same direction. This inhibits the tendency of the outer cone (air/water mixture) to collapse the inner cone (fuel spray) as is the case in the counter rotation swirl patterns and improves the circumferential uniformity of burning and thus prevents localized hot spots that manifest into the turbine. The water in the airstream does not collapse the fuel pattern and does not tend to conglomerate in individualize streams. Actual tests have shown a remarkable reduction in smoke emission during wet performance as compared with wet performance of heretofore known water injection systems.